Section 2 - Photosynthesis and water relations

BIOLOGIA PLANTARUM 34 (SUPPL.): 497-511;.1992

S E C T I O N 2 - P H O T O S Y N T H E S I S A N D W A T E R R E L A T I O N S

Plant responses to water stress

J. POSPi~ILOV~, Institute of Experimental Botany, Czechoslovak Academy of Sciences, Na Karlovce 1, 160 O0 Praha 6, Czechoslovakia

Biol. Plant. 34 (Suppl.): 497-499, 1992

Water stress is the most limiting environmental factor of growth of plants and agricultural productivity. Plant species or ecotypes are adapted to moist or dry localities, plants or their organs are acclimated to macro- and microclimatic conditions in which they grow, and plants respond to actual changes in air humidity or soil moisture. Different mechanisms were developed during plant evolution leading a) to avoidance of dangerous water deficit, and b) to tolerance of mild water deficit.

Water efflux is mainly controlled by the stomatal opening. The opening is regulated (feedback control) by the leaf water content. With the decrease of bulk leaf water potential below threshold value, the stomata close, even if other environmental conditions are optimal. In addition, two types of the feedforward control (the stomata are closed sooner than the mesophyll water potential is decreased) have been determined. The first of them is the direct response of stomata to air humidity which is associated with the peristomatal transpiration. The second one is response of stomata to the decrease of soil moisture and the rate of water absorption by roots (e.g. Jones 1990, Zhang .et al. 1990, Meinzer and Grantz 1991). The changes in gradients of water potential (especially of pressure potential) between guard cells and other epidermal cells, between epidermis and mesophyll, etc. operate in all types of stomatal regulation. Even the decrease in pressure potential in root xylem due to soil water deficit can be rapidly transmitted (pressure changes in connected bodies of water are transferred at the speed of sound) through the xylem to leaves and through apoplast to neighbourhood of guard cells (Matsuda and Rayan 1989, Boyer and Nonami 1990)/In addition, chemical regulation of transport of osmotically active substances (mainly K +) through guard cell membranes or regulation of production of osmotically active substances in guard ceils take part in the control of stomatal opening. In this regulation the most important is abscisic acid (ABA) and the root system can sense soil drying effectively by producing substantial amounts of ABA. Also further growth hormones, auxins and cytokinins (e.g. Mansfield and Atkinson 1990) or Ca 2+ ions (e.g. McAlnshet al. 1990) can operate in conjunction with ABA. Water deficit, and in consequence the production of ABA, also modifies the response of stomata to other factors, e.g. increases the sensitivity to internal CO 2 concentration. Similarly stomatal response to blue radiation is decreased under low air humidity.

The decrease in transpiration rate is always accompanied with the decrease in C02 influx. According to the theory of Cowan and Farquhar (1977) the stomatal regulation maximizing daily photosynthetic CO 2 influx for a given I-I20 efflux is considered to be "optimal". High water use efficiency is imi~ortant in crop monocultures. For wild plants, relatively low CO 2 influx is often sufficient, even if restricted CO 2 influx due to wate~ stress supports photoinhibition under high irradiance. C 4 pathway of CO 2 fixation is advantagenous for growth of plants under dry conditions, while under extremely dry conditions CAM predominates. In addition to decrease in CO 2 influx severe water stress also inhibited chloroplast activity. The mathematical models frequently used for distinguishing the stomatal and non-stomatal limitations to l~hotosynthesis were based on the assumption that the stomatal conductance is the same over the whole leaf blade. However, under certain environmental conditions (also under water stress or application of ABA) heterogeneity in

497

PHOTOSYNTHESIS AND WATER RELATIONS

stomatal opening ("stomatal patchiness") was lound (e.g. Raschke 1990). In conseqence, the stomatal limitation to photosynthesis is probably more important than it was assumed using the above mentioned m~xlels (e.g. Terashima et al. 1988).

Regulation of transpiration rate is significant also from the point of view of leaf energy balance in which an important role is played by leal movements. The transpiration rate is also restricted by inhibition of shtx~l growth, eventually by fall of old leaves. Simultaneously, the root growth is much less affected by water stress and so absorption capacity of roots per leaf area unit is increased (e.g. Sharp 1990).

Growth and many other physiological processes are mostly affected by pressure potential. Thus for plant tolerance to water stress the "osmotic adjustment" is important. Water potential is decreased due to a decrease in osmotic potential (by influx of mineral ions or production and transport of osmotically active organic substances) and not by decrease in pressure potential. Also "elastic adjustment" was found (e.g. Richter and Kikuta 1989). The stable pressure potential during water stress is reached by the changes in cell wall elasticity.

Drought can induce the transcription of mRNAs coding of a large number of proteins which under well watered conditions are not synthesized. Among them osmotin and its derivatives are the best known (Singb et al. Takeda et al. 1991).

Since about 2000 papers dealing with plant water relations and relative topics are published every year (see L6sch 1991, Pospf.~ilov~ and Solgu'ov~i 1992), only few chosen problems may be mentioned in this brief survey. From the new books e.g. Cherry (1989), Jones et al, (1989), Kreeb et al. (1989), and Davies and Jeffcoat (1990) can be recommended.

References: Boyer, J.S., Nonami, H.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to Shoot

Communication in the Responses to Environmental Stress. Pp. 45-52. British Society for Plant Growth Regulation, Bristol 1990.

Cherry, J.H.(ed.): Environmental Stress in Plants. Biochemical and Physiological Mechanism.- Springer-Verlag, Berlin-Heidelberg-New York-London-Paris-Tokyo 1989.

Cowan, I.R., Farquhar, G.D.: In: Jennings, D.H.(ed.): Integration of Activity in the Higher Plant. Pp. 471-505. Cambridge University Press, Cambridge-London-New York-Melbourne 1977.

Davies, W.J., Jeffcoat, B.(ed.): Importance of Root to Shoot Communication in the Responses to Environmental Stress.- British Society for Plant Growth Regulation, Bristol 1990.

Jones, H.G.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to Shoot Communication in the Responses to Environmental Stress. Pp. 81-93. British Society for Plant Growth Regulation, Bristol 1990.

Jones, H.G., Flowers, T.J., Jones, M.B. (ed.): Plants under Stress. - Cambridge University Press, Canlbridge-New York-Port Chester-Melbourne-Sydney 1989.

Kreeb, K.H., Richter, H., Hinckley, T.M. (ed.): Structural and Functional Responses to Environmental Stresses: Water Shortage. - SPB Academic Publishing, The Hague 1989.

L6sch, R.: Progress Bot. 52 : 35-60, 1991. Mansfield, T.A., Atkinson, C.J.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to Shoot

Communication in the Responses to Environmental Stress. Pp. 71-80. British Society for Plant Growth Regulation, Bristol 1990.

Matsuda, K.M., Rayan A.M.:In: Kreeb, K.H., Richter, H., Hincidey, T.M. (ed.): Structural and Functional Responses to Environmental Stresses: Water Shortage. Pp. 89-95. SPB Academic Publishing, The Hague 1989.

McAinsh, M.R., Browniee, C., Hetherington,'A.M.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to Shoot Communication in the Responses to Environmental Stress. Pp. l-11. British Society for Plant Growth Regulation, Bristol 1990.

Meinzer, F.C., Grantz, D.A.: Physiol. Plant. 83: 324-329, 1991. Pospf~ilov~i, J., Soifu'ov~i, J. (ed.): Water in Plants Bibliography. Vol. 16 (1990). - SPB Academic

Publishing, The Hague 1992. Raschke, K.: In: Pbaris, R.P., Rtxxl, S.B. (ed.): Plant Growth Substances 1988. Pp. 383-390.

Springer-Verlag, Berlin-Heidelberg-New York-Tokyo 1990.

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Richter, H., Kikuta, S.B.: In: Kreeh, ICH., Richter, H., Hinckley, T.M. (ed.): Structural and Functional Responses to Environmental Stresses: Water Shortage. Pp. 129-137. SPB Academic Publishing, The Hague 1989.

Sharp, R.E.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to Shoot Communication in the Responses to Environmental Stress. Pp. 29-44. British Society for Plant Growth Regulation, Bristol 1990.

Singh, J., Nelson, D.E., LaRosa, P.C., Bracker, C.E., Handa, A.K., Hasegawa, P.M., Bressan, R.A.: In: Cherry, J.H. (ed.): Environmental Stress in Plants. Biochemical and Physiological Mechanism. Pp. 67-87. Springer-Verlag, Berlin-Heidelberg-New York-London-Paris-Tokyo 1989.

Takeda, S,, Sato, F., Ida, K., Yamada, Y.: Plant Physiol. 97: 844-846, 1991. Terashima, I., Wong, S.-C., Osmond, C.B,, Farquher, G.D.: Plant Cell Physiol. 29: 385-394, 1988. Zhang, J., Gowing, D.J., Davies, W.J.: In: Davies, W.J., Jeffcoat, B. (ed.): Importance of Root to

Shoot Communication in the Responses to Environmental Stress. Pp. 163-174. British Society for Plant Growth Regulation, Bristol 1990.

Photosynthesis of the leaf and plant in a future, higher CO 2 atmosphere

j. ~,ANTRO~K lnstitute of Plant Molecular Biology, Czechoslovak Academy of Sciences, Branilovskd 31, 370 05 ~esk~ Bud~jovice, Czechoslovakia

Biol. Plant. 34 (Suppl.): 499-501, 1992

Anthropogenic increase of carbon dioxide content in atmosphere has manifold impact on individual plants, plant communities and the whole ecosystems (e.g. Bazzaz 1990, 1992). Serious impact on soil microbiota, on nitrogen fixing symbionts and rhizobia, and on herbivorous insects is expected. Thus, there is an increasing concern in plant response to higher CO 2 among plant ecologists, climatologists, soil microbiologists and entomologists. Changes in both crop and forest management are anticipated. The effect of increasing level of CO 2 in the atmosphere on physiology of carbon fixation and on closely related processes is summarized here.

In C 3 plants, the following processes were identified as the main physiological targets of the CO 2 increment: 1) short-term and long-term regulatory changes in carbon fixation, 2) changes in dark and light utilization of assimilates, sucrose or other assimilates allocation into expanding sink capacities, and 3) both direct effect of CO 2 and indirect effect of increasing assimilate pools on respiration. Consequently, changes in root/shoot ratio, increase in growth rate, rise in C/N ratio, enhancing quantity and changes in quality of root exudates and acceleration of plant development are observed. All these processes can be modulated by phosphorus or other nutrients availability (Harley and Sharkey 1.991) as well as by concomitant global warming (Farrar and Williams 1991).

Appart from knowing the huge amount of experimental data, addressing plant response to higher CO 2, two basic responses can be postulated: (i) Reducing photosynthesis to the processes controlled largely by behaviour of single enzyme (ribulose-l,5,-bisphosphate carboxylase/oxygenase - 'nabisco'), an increase in photosynthesis rate can be expected. Under saturated irradiance (and, thus, under non-limiting regeneration of ribulose-l,5,-bisphosphate, RuBP) and non-limiting nutrients, the increase in net photosynthesis rate (PN) should follow the Michaelis-Menten hyperbola known from enzyme kinetic theory. In the shaded plants, where the constraints by RuBP regeneration are expected, the increase in PN Can be explained by increasing carboxylation/oxygenation ratio as the substrate concentration for carboxylation rise. The underlying mechanism is inherent for nabisco the evolution of which occurred under at least ten-times higher CO 2 concentrations in atmosphere until cretaceous (Ehleringer et al. 1991). (ii) Viewing photosynthesis as a catena of many backward- regulated processes producing assimilates for plant growth and maintenance, one could find many negative feedback loops leading to complete plant insensitivity to increasing CO 2 in the extreme

499


case; e.g. capacities for water uptake and transport can be insufficient and 'selfdamage' of expanding plant ~xly in dry air could be envisaged: regulation of leaf internal CO 2 concentration by stomata closure mediated perhaps through photosynthate level is frequently observed: blocking of triose phosphate utilization can act as an end-product inhibition etc. Of course, combinations of many backward mechanisms are probable besides the hormonal direct action and regulation of gene expression. As a result, 'CO 2 acclimation' response (a long-term decrease in PN below the value observed immediately after the CO 2 concentration has been risen) is often reported. Stomata response to increasing C02: Usually, guard cells are regarded to be very sensitive to CO 2 through its inner cell side exposed into substomatal cavity (Mort 1990). CO 2 response of stomata combines probably two mechanisms opposing in their effect: first, inkibition of K + accumulation mediated by CO 2 effect on membrane permeability which is dominant mode of action, and second, supply of CO 2 as substrate for PEP-carboxylase producing malate in guard cells. The first mechanism results in stomata closure, the second one in stomata opening under increasing CO 2 levels. The dominancy results usually in stomata closure (Mansfield 1983). However, the analyses of relations among photosynthesis rate, stomatal conductance and internal CO 2 concentration as well as quantification of the CO2-feeedback gain of stomata lead to conclusions about low (if any) sensitivity of stomata to CO 2 (Wong et al. 1985, Farquhar et al. 1978). Stomata should response more to photosynthate stimuli transferred via epidermis then to CO 2 change transmitted through intercellular gas phase. Short-term CO, response in Pu and carboxylation: During several minutes after the CO 2 content w'as increased, dumping oscillatory response in PN is usually observed followed by an increased steady state value in PN (Sage et al. 1988). Higher steady state P~ reflects reduced competition from 02 for nabisco and, thus, reduced photorespiration rate. Surprisingly, activation state of rubisco has dropped in the Sage's experiments. The regulation of rubisco activity is not a direct effect of higher CO 2, which could cause e.g. carbamylation of lysine in reaction centre resulting in activation of rubisco. The drop in activity probably reflects limitation in RuBP regeneration induced by defficiency of ATP in shaded plants or by phosphate defficiency due to restricted triose phosphate utilization (Sage et al. 1988). Long-term CO, response in Piv and in utilization of assimilates: The initial mean increase in PN, induced by doubling of CO 2 concentration in atmosphere, was calculated to be 52 % for C 3 plants. However, the PN stimulation has dropped to 29 % in the average after a period of the high CO 2 acclimation (Cure and Acock 1986). Besides the above mentioned drop in activation state of nabisco, decrease in total nabisco concent was observed (Rowland-Bamford et al. 1991). Carboxylation rate transiently exceeds the rate of sucrose synthesis and export. Accumulation of starch grains in chloroplasts and chloroplast damage was also reported (Ehret and Jolliffe 1985). Appart from the widely accepted concent of the CO 2 acclimation, we can find the results of long- term (years) experiments which argue that the acclimation is an experimental artifact resulting from nutrient defficiency and from an inadequate space for the development of the root system (Ziska et al. 1990. Idso and Kimball 1991). Cure et al. (1987) did not find any acclimation response for soybean after three weeks of plant exposure to 700 I.tl CO 2 1-1. The rise in assimilates production was compensated by their utilization in dark after three days of exposition and then also by their utilization in light. Allocation into expanding sinks (root and stems) was observed in parallel.

The response of growth rate and of dry matter accumulation to elevated CO 2 is probably modified by the plant strategy. From 27 species rjative in British islands only competitors were highly sensitive to higher C O 2. The C O 2 effect decreased toward stress-tolerant or ruderal species (Hunt et al. 1991).

References Bazzaz, F.A.: Annu. Rev. Ecol. Syst. 21: 167-196, 1990. Bazzaz, F.A.: Sci. Amer. 222: 68-74, 1992. Cure, J.D., Acock, B.: Agr. Forest Meteorol. 38: 127-145, 1986. Cure, J.D., Rufty, T.W., Israel, D.W.: Bot. Gaz. 148: 67-72, 1987. Ehleringer, J.R., Sage, R.F., Hanagan, L.B., Pearcy, R.W.: Tree 6: 96-99, 1991.

5(X)


Ehret, D.L., Joiliffe, P.A.: Can. J. Bot. 63: 2016-2020, 1985. Farquhar, G.D., Dubbe, D.R., Raschke, K.: Plant Physiol. 62: 406-412, 1978. Farrar, J.F., Williams, M.L.: Plant Cell Environ. 14: 819-830, 1991. Harley, P.C., Sharkey, T.D.: Photosynth. Res. 27: 169-178, 1991. Hunt, R., Hand, D.W., Hannah, M.A., Neal, A.M.: Funct. Ecol. 5: 410-421, 1991. ldso, S.B., Kimball, B.A.: Plant Physiol. 96: 990-992, 1991. Mansfield, T.A.: Sci. Progr. 68: 519-542, 1983. Mott, K.A.: Plant Cell Environ. 13: 731-737, 1990. Rowland-Bamford, A.J., Baker, J.T., Allen, L.H., Bowes, G.: Plant Cell Environ. 14: 577-583,

1991. Sage, R.F., Sharkey, T.D., Seemann, J.R.: Planta 174: 407-416, 1988. Wong, S.-C., Cowan, I.R., Farquhar, G.D.: Plant Physiol. 78: 821-825, 1985. Ziska, L.H., Drake, B.G., Chamberlain, S.: Oecologia 83: 469-472, 1990.

Interrelationship between uptake of mineral ions and photosynthesis in submerged aquatic plants

L. ADAMEC institute of Botany, Czechoslovak Academy of Sciences, Dukelskd 145, 379 82 T:eboii, Czechoslovakia

Biol. Plant. 34 (Suppl.): 501, 1992

In four higher aquatic species with different ecological requirements for total alkalinity ("carbonate hardness") and different affinities to HCO 3- use, uptake of six ion species by leafy shoots was studied as dependent on a high or a very low photosynthetic rate, i.e., at a medium (7.5) or a high pH (10 or 9 or 8.8), and in darkness (pH 7.5). Apical segments (6-10 cm long) of CaUitriche hamulata (growing in soft waters, HCO 3" non-user), Elodea canadensis (wide range of waters, HCO 3" user), Ranunculus aquatilis (soft waters, HCO 3" user), and R. trichophyllus (hard waters, HCO 3- user) were used. The uptake of HPO42-, NO3-, CI-, K +, Ca 2+, and Mg 2+ was measured as a decrease in ion concentration of the solution (mM: NaHCO 3 - 1, CaCI 2 - 0.1, MgSO 4 - 0.1, KNO 3 - 0.3, Na2HPO a - 0.25) in 2-h periods, after which the solution was partly renewed. The pH of the solution in a stirred chamber (80 cm 3) was kept constant (+_-0.05), bubbling by gaseous CO 2 and CO2-free air and a pH-stat were used. The species growing in hard waters (E canadensis and R.trichophyllus) took up all the ion species at a higher rate at a low photosynthetic rate than the soft- water species (C. hamulata, R. aquatilis) did, it also held for FIPO42- and NO 3" at a high photosynthesis. This difference in ion uptake at a high pH (very low uptake of carbon) could have an ecological significance when soft-water species compete strongly for inorganic carbon, especially in HCO 3- non-users. In all species, the uptake of HPO42-, NO3", CI-, and Mg 2+ did not depend markedly on the photosynthetic rate. The uptake of K + in all species was distinctly higher at a high photosynthesis and even a profound K + effiux from plants was found in darkness. Except of C. hamulata, a small uptake of Ca 2+ prevailed at a high pH, whereas a Ca 2+ efflux prevailed at the pH of 7.5 both in light and darkness. Obviously, the Ca 2+ fluxes in both directions included mostly the apoplast (CaCO 3 incrustation of cell walls).

501


Effect of water stress and different mineral nutrition on plant water relations of cereals

M. BRESTI(~, M. ZIMA, R. HOJ(~U~, M. HUDECOVA Universi~ of Agriculture, 949 76 Nitra, Czechoslovakia

Biol. Plant. M (Suppl.): 502, 1992

Effect of different stressors (polyethylenglycol, mannitol) was studied in laboratory experiments on young spring barley plants (Hordeum vulgare L.) and on some other cereals. Changes of plant water parameters are quantified (transpiration, water content, leaf diffusion resistance, water saturation deficit) in relation to the growth rates of the individual organs of the plant. Deficit of the main mineral elements (N,P,K) influenced more expressively the initiation and growth of the leaves, their active life duration, leaf diffusion conductance than N,P,K surplus. The possibilities for formulation of monitoring of the load levels by stressors through expeditive methods as well as possibilities for the elimination of negative ecological situations and stability of plant physiological processes are discussed.

Photosynthesis under conditions of in vitro cul ture

J. (~ATSK~' and J. SOLAROVA. Institute of Experimental Botany, Czechoslovak Academy of Sciences, Na Karlovce 1, 160 00, Praha 6, Czechoslovakia

Biol. Plant. 34 (Suppl.): 502-503, 1992

Photosynthetic activity of plantlets grown autotrophically or mixotrophicaUy on agar substrate in vitro is frequently limited by low carbon dioxide concentration and low irradiance during the light period, and affected by high air humidity, increased ethylene concentration, etc. The limitation of net photosynthetic rate (Pr~) by low CO 2 concentration then leads to a considerable reduction of growth (Sol,royal 1989). Daily carbon gain (24 h) of autotrophic plantiets cultivated in vitro using a standard procedure decreased - in dependence on saccharose concentration in the medium - to 25 - 10 % of that in control plantlets cultivated under atmospheric CO 2 concentration (tobacco, carnation). CO 2 concentration in cultivation vessels for about 80 % of light period approached CO 2 compensation concentration (F) and PN was near to zero. Considerable limitation to PN resulted in a similar limitation to growth rate measured as the rate of dry matter accumulation. In spite of very low PN in cultures in vitro (measured in situ) the photosynthetic apparatus was fully developed. The limitation to PN by CO 2 deficiency was confirmed also by a 200 % increase in dry matter accumulation after increasing CO 2 concentration in cultivation vessels. The difference in dry matter accumulation between plantlets grown under atmospheric and increased CO 2 concentration was more pronounced on medium without saccharides. Limitations to photosynthesis under conditions in vitro were studied in model experiments: Environmental conditions in cultivation vessels were simulated by growing French bean (Phaseolus vulgaris L.) plants in nutrient solution in closed vessels under high relative humidity of air (90%) and CO 2 concentration decreasing with the development of photosynthetic activities during plant ontogeny (1200 to 300 mg m't). The ontogeny of model plants was more rapid, primary leaves reached photosynthetic maturity 2 to 3 d earlier and their life span was 7 to 14 d shorter. Photosynthetic activity in situ of these plants was limited, after reaching "photosynthetic maturity", similarly to plants grown in vitro. When measured ex vitro, however, 50 to 70 % higher Pr~ was found in leaves of different ages as compared with plants grown in vitro under atmospheric CO 2 concentration (600 mg m "t) and lower relative humidity of air (40 to 60 %). The increase in Pr~ was connected with a very high epidermal conductance for CO 2 transfer and with low reactivity of stomata. The rates of dark and light

502


respiration as well as CO 2 compensation concentration were I 0 to 30 % lower in plants grown under conditions simulating the culture in vitro.

Reference: Sol,oval, J.: Photosynthetica 23: 100-107, 1989.

Stomatai behaviour of an invasive annual (Impatiens parviflora DC.) in natural habitats, SW Slovakia

P. ELIA~ Institate of Botany, Slovak Academy of Sciences, Ddbravskd cesta 14, 842 23 Bratislava, Czechoslovakia


Impatiens parviflora is an erect annual of Central-Asiatic origin, introduced into Europe in the 19th century, and now invading forest communities in Central Europe. It was considered as a shade- tolerant plant or as a facultative sun plant, being an extremely phenotypically plastic species. In summer months (July, August) of 1984-1987, stomatal resistance (rs) was measured by Li-Cor porometer, in course of .several sunny days, in plants growing in some Impatiens populations near Bratislava (Mal6 Karpaty Mts: Z.elezn~i Studienka, Biely Kr/~) and at B~tb (formely I.B.P, Forest Research Site), SW Slovakia. The Impatiens populations in forests, at forest margins (edges) and on clear-cut areas differed by size (height, biomass) and architecture of plants but also in density, size and arrangement of stomata (hypostomatic versus amphistomatic leaves). Stomatal resistance of the Impatiens species varied predominantly in relation to light conditions of the habitats (sunny places, light-flecks, semi-shade, deep shade) and water-saturation status of the leaves. In all habitats daily rs-curves were close to the U-type-curves but rs-values were usually lower in plants growing at forest margins than in forest-growing plants. In a forest stand, noon values ofr s varied around ca 5 s cm -~, while at forest margins they were usually lower than 4 s cm "1. The relationship between stomatal conductance (ks) and photosynthetically active radiation (PhAR, I.tmol m -2 s -1) was analysed by the boundary-line method. It was found that at similar PhAR values, higher k s occurred in plants growing at forest margins (maximum ks - values were higher than 0.5 cm s-a), in comparison with plants growing in the forest stand (k s max. ca. 0.25 cm s'l). In hot summer days (drought, high temperature) plants growing in sunny places (forest margins, woodland clearings) were stressed and higher r s - values were found than in forest-growing plants.

Stomatai conductance and transpiration rate of tall poplar trees in a flood-plain forest by the Danube river, SW Slovakia

P. ELIA~, J. NAVARA Institute of Botany, Slovak Academy of Sciences, Dtlbravskd cesta 14, 842 23 Bratislava, Czechoslovakia

Biol. Plant. 34 (Suppl.): 503-504, 1992

in an 11-year-old and 28.6 m high (in average) stand of poplar (Populus euramericana, cv. Robusta) at Gab~fkovo 0ocality Kr"aiovskfi Itlka, SW Slovakia), transpiration rate (TR) and stomatal conductance (gs) were measured by LI-1600 Steady State Porometer in crowns of tall trees in the courses of 10 d from July to October 1991. To measure the TR and gs in crowns of the trees, a 30 m high steel-tube tower was built up around the sample poplar tree (dl, 3 = 30.7 cm, h = 31.5 m, total leaf area 249 m2). Variations in measured parameters within the crown were analysed in relation to aspects (S, E, N, W), levels (upper, lower), current-shoot types 0ong, short) and sides of

503


amphistomatic leaves (abaxial, adaxial). Maximum TR and gs was usually found in the upper crown level, west (July to August) and south (August-September) aspr and in the long shoots, and in abaxial epidermis (lower side of a leaf), and it was usually higher than 10 tag cm "2 s -1 and 12.4 mm s -1, respectively. In the lower crown levels, TR and gs were usually lower than 5 tag cm "2 s "t and 7.5 mm s "l, respectively. Hourly values of transpiration per tree increased up to 80 1 (at noon) and daily values of transpiration per tree varied, in summer, between 256 and 661 1 of H20. It is evident that the annual summ of transpiration of the poplar stand (stand density was 247 trees per ha) is higher than 1200 mm H20. The measurements have been a part of monitoring of the forest environment changes induced by construction of the G a b ~ o v o Dam on the River Danube. The results will be used by the Centre of Environment Monitoring at the Slovak Commission of Environment (SKZP) in Bratislava.

Stonmtal regulation of the winter wheat transpiration daily course

J. HUZUL,~.K*and F. MATEJKA** Irrigation Research Institute, Vrakunskd~ 29, 825 63 Bratislava, Czechoslovakia* Geophysical Institute, Slovak Academy of Sciences, Dlihravsktt 5, 842 28 Bratislava, Czechoslovakia **


It follows from Penman-Monteith equation for transpiration, that transpiration rate (E) falls sharply as stomatal resistance (rL) increases, if atmospheric conditions and soil moisture contem are kept constant. There is, however, a lot of experimental data in literature showing that daily maxima of E do not correspond to daily maxima of r L. The aim of the paper is to analyse and support this paradox using a verified mathematical model of winter wheat water regime. Daily courses of r L for low and high air evaporative demands (water vapour pressure deficit maximum during the day 1003 and 2(k')O Pa) were analysed. It follows from the analysis, that the daily course of r E at nonlimiting soil moisture content is simple, with one minimum between 9.00 and 10.00 a.m. If we decrease soil moisture content during the simulation, a strong local maximum of r E dally course appears at about midday. In spite of this, transpiration is maximal at midday as well. Such situation occurs, because the relationship between E and r E is not functional. From 6.00 to 9.00 a.m. E falls as r E increases, hut later it increases. The increase of r E is accompanied by sharp increase in leaf water potential absolute value, which causes the maximum E to he at midday. It also follows from the analysis, that changes in leaf water potential depend on changes in stomatal resistance and not vice versa.

Daily course differences of transpiration rate for soybean cultivars

A. KUBOV,6.* and J. NAVARA** Department of Plant Physiology, University of Agricultare, A. Hlinku 2, 949 76 Nitra, Czechoslovakia* Botanical Institute, Slovak Academy of Sciences, Sienkiewiczova 1, 842 23 Bratislava, Czechoslovakia**

Biol. Plant. 34 (Suppl.): 504-505, 1992

The transpiration rate (TR) was measured for 6 soybean cultivars (Dunajka, Sluna, Zora, Alda, McCall, Maple Arrow) in R-5 stage during summer sunlight day in field conditions by Steady-State porometer LI-1600. Values of PhAR, leaf and air temperatures and stomatal resistance were recorded simultaneously. Significant differences of water relations were obtained for tested cultivars. TR of Canadian cultivars were lower with smaller variations during day time than TR of the domestic one. All domestic cultivars showed the first highest maximum TR between 11-12 h

504


a.m. Aftern(xm inhibition TR differ for individual cultivars. Cultivars Dnnajka, Siuna and Zora were strongly inhibited (up to 40 % of maximum), whereas Aida, McCall and Maple Arrow were inhibited only a little. The second TR maximum was recorded at 16:30 or 17:30 h with high peaks for cultivars McCall, Sluna and Zora. Cultivars Aida, Dunajka and Maple Arrow had lower second peak of TR. These cultivars have very low values of stomatal resistances with small fluctuation amplitudes. The lowest alternations of leaf water content were obtained in cv. Dunajka and Sluna. Leaf temperatures were 1-2 ~ higher than air temperatures during day, after 17:00 h leaf temperature was lower than the air temperature.

Chlorophyll content, C02-exchange and plastid structure of the saprophyte Neottia nidus-avis (L.) L.C. Rich.

E. MASAROVI(~OV,6,, A. LUX and J. HUD,AK Department of Plant Physiology, Faculty of Natural Sciences, Comenius University, Ml~nska Dolina B-2, 842 15 Bratislava, Czechoslovakia


Neottia nidus-avis has been attractive for botanists since the last century because of its special appearance and biology. It is especially known for the rapid coiour change of the inflorescence from brown to green following immersion in methanol or hot water. Stomata are reported to only be found on tepals. Our observations confirmed the presence of stomata on these same organs and then only in very low frequency. Some early work claims that this plant has low photosynthesis at low irradiance, however, a subsequent study questions this conclusion (Reznik 1958). Our study showed that whole plant photosynthesis actually reached negative values and the dark respiration also was low. In both normal (brown) and albino forms no CO 2 fixation occurred. These findings, together with the observation that both forms display essentially identical vitality led to the conclusion that Neottia nidus-avis is a true holosaprophyte (Reznik 1958). However, the same and other authors found only chlorophyll a in this species. In our measurements we also found chlorophyll a (0.7388 mg g-~) but in addition, a very low level of chlorophyll b (0.058 mg g-l) was detected. Structural studies of this species reveal several interesting features. Reznik (1959) observed the presence of starch in both the brown and the white forms of Neonia. Later observations demonstrated spindle- like plastids in tepals. EM studies showed coiled and branched thylakoids, plastoglobuli as well as starch in flowers and stalks. Our observations confirmed all of these structures in plastids of tepals. But apart from this, we found another type of unusual plastid in stalk scales. These plastids contained dark (electron dense) bodies which were penetrated by regularly distributed tubes. The function of these newly discovered structures is, as yet, unknown.

Reference: Reznik, H.: Planta 51:694-704, 1958.

Leaf photosynthetical capadty of high-productive hybrids of maize (Zea mays L.) grown under field conditions during generative stage of ontogeny

P. MODRY and L. JURA(~EK ZEAINVENT, Breeding and Research Institute, Trsffnska 1, 917 52 Trnava, Czechoslovakia

Biol. Plant. 34 (Suppl.): 505-506, 1992

The place of maize leaf photosynthesis in productional process and its improvement by means of selection and breeding is a frequently discussed problem which is closely connected with knowledge of photosynthetical potentionality. Therefore in the years 1986-1988 we decided to analyse a term of

505


high and low net photosynthetical rate (PN) through the measurement of photosynthetical capacity (PC) on the middle part of leaves in the positions -2, +1, +4 (0 = the nearest leaf to the main ear). The selected maize hybrids (CE 185, DEA, CE 420) were grown in two different densities (84 000 and 119 000 plants per ha). The PC of intact leaves was measured in 3 cycles with an open gas exchange system with IRGA under constant laboratory conditions (pbotosynthetical photon flux density-PPFD-varied from 210 to 2130 p.mol m -2 s -j) during the generative stage of ontogeny. In another experiment in 1991, we measured the actual PN of the middle part of leaves in the position + 1 of the hybrid TA-TO 260 S by/2-6000 in field conditions (3 densities, 3 levels of applied N, with and without irrigation). From the first experiment it resulted that PC of the measured leaves (all hybrids) in both densities was high and comparable. The highest value of PN in the first experiment was 2.263 mg (CO 2) m "2 s "1 (PPFD 2130 Ilmol m-; s -1) and that in the 1991 experiment was 2.067 mg (CO 2) m "2 s -1 (PPFD 1725 ttmol m "2 s'l). In the first experiment, the term "high and low Pr~" in the productional process is specified by means of "light curves" of photosynthesis. Comparison of the maximum PN values in our experiments with those indicated in foreign works and measured under adequate conditions shows that the current high-productive hybrids probably do not differ in potential possibilities of PN.

Water potential of styles and unilateral interspecific incompatibility in Solanaceae

J. POSP[~ILOVA, V. 2ARSK~', L. ~TRBAI~OVA, L. ~HOVA and J. TUPY Institute of Experimental Botany, Czechoslovak Academy of Sciences, Na Karlovce 1, 160 O0 Praha 6, Czechoslovakia


In unilateral interspecific incompatibility, the pollen tubes of self-incompatible (SI) species grow through the styles of self-compatible (SC) species, while in reciprocal crosses the growth of pollen tubes of SC species is inhibited in the styles of SI species. The mechanism of these relations in the family Solanaceae was studied from the aspect of possible role of stylar water potential. Elongation growth of pollen tubes in intercellular spaces of transmitting tissues of styles requires a relatively large water uptake and is thus dependent on water potential gradient between the growing tube zone and the stylar tissue. In the SI apecies Nicotiana alata and Petunia hybrida the stylar water potential (measured by Wescor Dew-Point Hygrometer) was considerably lower and at the same time also the stylar water content (in % of fresh mass) was lower in comparison with the water potential and water content in the styles of SC species Nicotiana sylvestris and Nicotiana tabacum. During ontogeny of flower buds the stylar water potential in N. alata decreased more expressively than in N. tabacum. The pollen tubes of SI and SC species exhibited different requirements for concentration of osmotica (saccharose or polyethylene glycol) in medium during in vitro germination. The optimum growth in vitro of pollen tubes of N. alata and P. hybrida was achieved at lower water potential of medium than the optimal growth of pollen tubes of N. sylvestris and N. tabacur~ The higher peroxidase activity determined in transmitting tissue of styles in SI species in comparison with SC species might be also connected with the lower stylar water potential in SI species than in SC species. Therefore one of the unspecific mechanisms of incompatibility in Solanaceae might consist in growth inhibition of pollen tubes of SC species in too "dry" transmitting tissue in the styles of S1 species.

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The direct effect of abscisic acid on photosynthesis is not an artifact

J. ~ANTRI~I(~EK, M. HRONKOV./~ and M. ~IMKOV.A Institute of Plant Molecular Biology, Czechoslovak Academy of Sciences, Branigovskd 31, 370 05 ~esk~ Bud~jovice, Czechoslovakia


The non-stomatal effect of abscisic acid (ABA) was established in in vitro cultivated plants under premise that ABA is not able to close stomata of in vitro cultivated plants. In vitro tobacco plants (Nicotiana tabacum cv. White Burley) cultivated on MS agar medium without phytohormones and sucrose in glass vessels covered with alluminium foil were used for experiments. The plants were cultivated under constant temperature 20 ~ and 12 h photoperiod for 2 months. Photosynthesis (Ps) and transpiration (E) rates of adaxial side of the detached leaves were measured using an adapted 1.2-6200 photosynthesis system (LI-COR, USA) with 250 cm 3 leaf chamber. Simultaneous leaf surface temperature measurement were done by IR camera (NEC-SAN E1 6T62, Japan) hermetically connected to the leaf chamber by a cylindrical glass adapter. The leaf exposed in the dark for 15-30 min was then illuminated. The kinetics of light induction of photosynthesis was typical for in vitro cultivated plants: PN reached a maximum 8 to 15 rain after switching the light on, then the constant or slightly decreasing Ps was observed for 30 to 50 rain. In contrast to plants adapted to atmospheric conditions, plants growing in vitro showed nearly constant E for darkened and illuminated leaf. Thus, the kinetics of Pr~ reflected probably the process of light induction of the enzymes of Calvin cycle and was not modulated by stomata opening. The leaf surface temperature measured by IR camera in dark ranged in the central part of the leaf from 20.2 ~ to 20.5 ~ after switching the light on, a non-uniform temperature increase was observed (the increase ranged from 2.4 to 3.4~ Feeding with ABA (5 ~tl 10-2M ABA solution into petiole of the leaf) has only very small effect on E as well as on leaf surface temperature (E increased for about 5% during 3 rain following the ABA application and then fell down steadily to 82 % of its original value during the next 25 rain). Temperature average over the leaf surface slightly decreased. In contrast to E and temperature, Pr~ showed dramatic transient fall followed by recovery to 70 % of the initial Pr~ values. Where the feeding with ABA was continuous, PN fell down to zero without recovery. The results support the hypothesis, that stomata of in vitro cultivated plants are not sensitive to ABA and that ABA affects photosynthesis directly, not only through stomata closure. Mechanism of this effect is not known at present.

Response of photosynthetic apparatus to periodic CO 2 deficiency in two potato cultivars

J. ~ANTRI~I(~EK, g. ROH,~(~EK, P. ~IFFEL, V. KONE(~N./~ and M.E. BAROJA Institute of Plant Molecular Biology, Czechoslovak Academy of Sciences, Branigovsk~ 31, 370 05 ~es~ Bud~jovice, Czechoslovakia

Biol. Plant. 34 (Suppl.): 507-508, 1992

Two potato cultivars (Solarium tuberosum L., cvs. Kennebec and Jaerla) differ in their ability to survive a transfer from in vitro to normal ex vitro cultivation. Cultivar Kennebec (cv. K) acclimatizes very well while cv. Jaerla (cv. J) exhibits a great percentage of mortality. The periodically fluctuating CO 2 concentration in glass vessels during the light and dark periods was previously hypothesised (~antr~ek et aL 1991) to cause changes in radiant~em~'gy utilization. The explants were grown autotrophically in glass vessels covered with an allumihium foil for one month at 20 ~ under photon fluence rate of 60 - 80 p.moi m -2 s -1 during 12 h photoperiod. Then the vessels were hermetically closed. For 11 d, simultaneous measurements of CO 2 exchange and of

507


chlorophyll fluorescence emission were made using LI-6250 IR gas analyzer (LI-COR, USA) and PAM-fluorimeter (H. Waltz, Germany). The effect of O2-free atmosphere was investigated. The inhibitory effect (IE) of 02 on CO 2 fixation was very high (23-67 % of the photosynthetic rate in O2-free atmosphere) immediately after the closing. It was valid for both CO 2 concentrations under which IE was investigated (close to F and 450 cm a m'a). The CO 2 starvation resulted in the flattened CO 2 response of net photosynthetic rate (PRO, in an increase of CO 2 compensation concentration (1"3 and in a quick decrease (on the 5th d) and even in an elimination (on the 1 lth d) of O 2 effect measured at higher CO 2 concentration. The drop in IE was quicker then the depression in PN. On the contrary, IE estimated at CO 2 concentrations close to F increased after the full stop of CO 2 supply. The fluorescence parameters �9 e (the quantum yield of PS2 electron transport), qo, qE and ql (the photochemical, non-photochemical and photoinhibitory quenching, respectively) were used to monitor differences between both cultivars in their photosynthetic activity. From the same starting value of Oe=0.52 for both cultivars decreased ~e on the 5th d to 0.38 (cv. K) and to 0.26 (cv. J). A higher reduction o f * e in cv. J brought about a decrease in qo (on the 11 th day of 0.68 cv. J and of 0.86 cv. K). There was observed a significant difference in qE (in cv. J every time higher by 20-30 %) and large decrease in ql after the 5th d (from ca. 0.75 to. 0.53). The adaptation mechanisms (e.g. fotorespiration and fotoinhibition) enable the plants to dissipate non-destructively excitation energy absorbed. Under the CO 2 deficiency, these mechanisms reflect the higher surviving ability of cv. Kennebec.

Reference: ~antr~ek, J., ~iffel, P., Poligensk~, M., Pegkov$, H.: Photosynthetica 25: 203-208, 1991.

Effect of water and temperature stresses on some cereals

J. ~VIHRA Department of Plant Physiology, University of Agriculture, A. Hlinku 2, 949 76 Nitra, Czechoslovakia


Water deficit at the end of the stem elongation phase caused changes in flag leaf chloroplasts, influenced gradual formation of sclerenchymatous tissues and thickening of leaf epidermis. The diameter of tracheids was decreased. Water and temperature stresses during first phase of grain mass accumulation reduced the grain mass, during the second phase the grain mass reduction was depended on the species and cultivars and reached 20-35 %, and in the third phase the reduction was 5-12 %. The average maximal grain (sink) mass was decreased from 42.6 to 37.5 mg in barley and from 49.2 to 43.6 mg in winter wheat. The maximum sink size was in barley ear on the 8th and 9th grain and in winter wheat on the 7th and 8th spike. The liner correlation coefficient between ear length and ear grain number was decreased from 0.851 to 0.488 in water stressed plants closely before anthesis and repeated stress after anthesis reduced this correlation coefficient to 0.425.

The effect of global radiation intensity and water vapour pressure deficits on soybean (Glycine max (L.) Merr.) water regime characterist ics

M. VA~KOV,~ Irrigation Research Institute, Vrakunsk6 cesta 29, 825 63 Bratislava, Czechoslovakia

Biol. Plant. 34 (Suppl.): 508-509, 1992

Using a mathematical model, the relationship between meteorological factors and soybean water regime characteristics 0ear water potential, canopy resistance, actual transpiration to potential

508


transpiration ratio) was evaluated. Results after three years of measurements of leaf water potential, stomatal resistance and global radiation were used to find values of parameters in the model. Aim of this work was to describe the effect of water vapour pressure deficit and irradiance on soybean water regime. It was shown, that water vapour pressure deficit is an important ecological factor. Its relationship to canopy resistance is quadratic, and therefore it significantly affects soybean canopy water regime. Analysis of the relationship between water vapour pressure deficit and transpiration rate has shown that maximal transpiration rates were observed at water vapour pressure deficits 1000-1500 Pa. At lower or higher deficits transpiration rate falls and it cannot be changed by changing soil water content. Irradiance affects canopy or stomatal resistance differently at different soil water contents. In wet soil (soil moisture 30 %) stomatal resistance decreases with increasing irradiance, as expected. In a dry soil (soil moisture 15 %) stomatal resistance increases in parallel with irradiance.

Photosynthetic rate at different temperatures in relation to cold acclimation

M. VEDRALOVA Research Institute of Crop Production, Drnovskd 507, 161 O0 Praha 6, Czechoslovakia


Plants of winter wheat (Triticum aestivura L., cv. Mara) were grown in Hoagland 3 nutrient solution in controlled conditions. The photoperiod was 14 h, with photon flux density of 300 ~tmo1-2 s -1, at a day/night temperature of 15/12 ~ When the area of the second leaf was fully developed, plants were transferred to 5 ~ for cold acclimation. Other cultivation conditions were identical as described above. The CO 2 gas exchange rate was measured by the infra-red CO 2 analyzer URAS 3G in an open gas exchange system, the rate of transpiration was measured by a psychrometer. The CO 2 exchange rates were measured at the photon flux density of 500 ~tmol "2 s "~, the leaf temperature of 5 ~ and 20 ~ the 02 concentration of 21% and at the outlet concentration of 350 cm3r ) m "3 . The aim of these measurements was to find out the time necessary for acclimated and nonacclimated plants to reach the photosynthetic steady-state rate at different temperatures. The plants were taken from the growth cabinet in dark period and ten attached fully developed second leaves were placed into the assimilation chamber for dark adaptation (60 min at 5 ~ 20 min at 20 ~ The nonacclimated plants reached the photosynthetic steady-state rate after 60 rain of the light period at 5 ~ (10 I.tmol "2 s "l) and during the next 6 h no changes were found. The plants measured at 20 ~ reached the photosynthetic steady-state rate in 20-40 min (19.5 p.mol "2 s'l). As the period of cold acclimation increased the time necessary for reaching the photosynthetic steady-state rate also went up. After 3-4 weeks of cold acclimation this time increased to 3 h, when measured at 5 ~ (7.5 Ixmol "2 s "l) and to 7 h, when measured at 20 ~ (15.5 p.mol "2 s'~). In measurements at 20 ~ the rates changed in the following way: after 1 h 2 1 % , after 2 h 43 %, after 3 h 64% of the photosynthetic steady state-rate. The prolonged time period necessary for the stabilization of the photosynthetic rate of cold acclimated plants measured at 5 ~ is probably due to assimilate accumulation and due to increased viscosity in intracellular space. At the same time a two fold increase in dry mass per unit leaf area was found. Acclimated plants measured at 20 ~ were affected in the same way, but also at the same time the increased temperature resulted in deacclimation. There is no problem when we measure the plants at the same temperature, as that in which they are cultivated, but if the temperature during measurement is different from cultivation conditions the plants are found to have adapted to the altered conditions. The adaptation of cold acclimated plants (at 5 ~ to 20 ~ in the assimilation chamber is much faster than the adaptation of nonacclimatized plants (at 15 o C) to 5 ~

509


Responses of stomata to ABA, IAA and carbon dioxide in isolated epidermis of Viciafaba L.

M. VICHERKOVA and M. I~I(~ANEK Department of Plant Physiology and Anatomy, Faculty of Science, Masaryk University, Kotld~skd 2, 611 37 Brno, Czechoslovakia


Stomatal regulation is controlled by external and internal factors such as light, temperature, humidity, K + concentration, some phytohormones, etc. Contradictious views on the effect of phytohormones and their interactions expecially under different ambient conditions still exist. The effects of abscisic acid inducing the closure of stomata and l~-indolyl-3-acetic acid inducing their opening are well known. Currently, ABMCO 2, IAA/CO 2 and ABA+IAMCO 2 relations still remain an open question. All experiments were made by the method of isolated abaxial epidermal strips incubated in standard medium of 10 mol m "3 MES buffer pH 6.15 in constant conditions (temperature 25 + 1 ~ photon flux density 120 I.tmo1-2 s -1, relative humidity 98%) in the presence (350 I.tmol mol "1) or absence of CO 2 during 3 h illumination. KCI (50 or 100 real m'3), ABA and IAA (10 "5 to 1 real m -3) were incorporated singly or in combination into buffer. Epidermal strips being incubated in the buffer alone showed the stomatal apertures to be significantly smaller in the presence of CO 2, it acted as inhibitory agent on stomatal apertures. When CO 2 interacted with ABA stomata remained more open and the closing effect of CO 2 did not appear. ABA-induced closure of stomata was thus diminished. IAA stimulated stomatal opening; in CO 2 presence stomatal apertures were decreased in contrary to its interaction with ABA. The closing effect of CO 2 remained maintained but 1AA was able to decrease it. At the simultaneous action of both phytohormones IAA limited the inhibitory effect of ABA but the way of interaction between CO 2 and ABA in the presence of IAA in incubation medium was maintained and its counteracting influence against ABA did not appear. The experiments revealed the existence of a complicated interaction among used phytohormones and CO 2, the possibility of changing in the way of these interactions by means of agent combinations as well as the fact that phytohormones were important regulators of the stomatal activity.

The changes of water relations and photosynthesis of barley after absdsic acid application

M. ZIMA, M. BRESTI~, R. HOJ(~U~ and M. HUDECOVA Department of Plant Physiology, University of Agriculture, A. Hlinku 2, 949 76 Nitra, Czechoslovakia


Abscisic acid (ABA) was added to the hydroponic solution in total concentration of 10 -4 M to the hydroponically grown young (14 - 28 d old) spring barley plants (Hordeum vulgare L.). Changes of leaf diffusion conductance, transpiration and photosynthesis rates were measured by LICOR-6200 as well as water uptake and water content in individual plant organs. The onset of ABA starts immediately after addition with slight increase of PN and conductance values followed by their decrease due to stomata closing. Individual cultivars react to ABA treatment differently. The most stabilized values had shown cv. Bonus, though its total decrease of PN and conductance values was up to 40 % of its maximal values. Dwarf cultivar KM-341 reacts intensively to the ABA treatment.

510


Influence of water regime on the realisation of yield potential and on the length of potato vegetation period (Solarium tuberosum L.)

J. ZRUST Research institute of Potato, Dobrovskdho 2366, 580 03 HavlidCk~v Brod, Czechoslovakia


The production of biomass and in this connection also the production of plants is very often limited by the water deficit. Concretely in potatoes it is one of the factors, which limit mostly the yield. Its lowering appears in three ways. It reduces the dry matter production directly and by means of the lowering of the rate of photosynthesis. It limits the development of the crop (the size of leaves) and by this indirectly the dry matter production. It accerelates also the senescence of the crop. The study of water regime was carried out in controlled conditions of pot experiments in greenhouse. For the experiment we chose 4 varieties with different length of growth period: Resy - very early, Radio - medium early, D6sir6e - medium late, Karnak - late. During the vegetation period we submitted in different growing phases a part of plants to "a middle" (50% RSM - relative soil moisture) and to "a sharp" (35% RSH) stress. The drought delayed the emergence directly in proportion to its intensity. It lengthened growth phases and with this also the total length of vegetation period, if the water stress functioned at the beginning and in the futtber course of vegetation. On the contrary it shortened the vegetation period, if the drought took place at the end of vegetation period before the entrance into the physiological maturity of the crop. The drought at the beginning of vegetation period positively influenced the height of plants and the leaf area. It confirmed our previous estimation, that plants adapted to the drought in the phase of emergence are most productive. The water deficit in soil during the vegetation period caused more rapid old growing of haulm with the rate of photosynthesis proportionally to its height. The highest yields of tubers was estimated in variants with 50 and 35 % RSH in the phase of planting to the emergence.

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Documents

Section 2 - Photosynthesis and water relations